Electrical Specification and Lighting Design in London Renovations

Electrical work is the circulatory system of a renovation. Every other system — HVAC, AV, security, lighting control, EV charging — depends on it, and unlike most other trades the electrical installation is largely invisible once walls are closed. Decisions made during first fix cannot be easily revisited. This makes the electrical specification one of the highest-stakes early-stage decisions in a prime London renovation.

Consumer Unit Sizing and Incoming Supply

Incoming supply assessment:

Most London Victorian terraces were connected to the grid with a single-phase 60A or 100A supply — sufficient for the electrical loads of the original building and modest modern additions, but potentially inadequate for a heavily renovated home with a heat pump, EV charger, electric oven, and underfloor heating simultaneously.

The first step in any major electrical specification is an assessment of the existing incoming supply capacity and the projected maximum demand of the renovated building. A load calculation (by the electrical designer or M&E engineer) determines whether the existing service cable and meter tails are adequate or whether a new service connection is required from the DNO (Distribution Network Operator — typically UK Power Networks in London).

A new DNO connection — larger service cable, new meter, larger cut-out — takes 6–20 weeks to arrange and costs £500–£5,000 depending on the extent of work. It must be initiated early, before the renovation programme is committed.

Three-phase supply:

For large properties or those with significant electrical loads (heat pump, pool plant, EV chargers, large AV systems), a three-phase supply (400V, 3-phase + neutral) provides both additional capacity and the ability to balance loads across phases. Three-phase supply is available in most London streets but not universally — check availability with UK Power Networks at the start of the project.

Consumer unit (distribution board) specification:

The consumer unit must be sized for the actual number of circuits required in the renovated property, plus a 30% spare capacity for future additions. A thorough prime London townhouse renovation typically requires:

• —20–40 lighting circuits (one circuit per 6–8 points, or per zone for lighting control systems)
• —15–25 socket ring circuits and radials
• —Dedicated circuits for each major appliance: oven, hob, dishwasher, washing machine, tumble dryer, fridge/freezer
• —Dedicated circuits for each HVAC unit
• —Dedicated EV charger circuit (7kW or 22kW)
• —Alarm and security circuits
• —Spare ways for future additions

A standard 20-way consumer unit is rarely adequate for a prime London renovation. A 40-way or dual-board arrangement is more typical. All consumer units must comply with BS 7671 (IET Wiring Regulations, 18th Edition) and be RCCB-protected.

First Fix: The Critical Phase

First fix electrical — the installation of containment (conduit, trunking, cable tray), back boxes, and wiring — must be completed before plastering. This is the phase where all routing decisions are made. Key coordination requirements:

Cable routes:

All cable routes must be agreed with the architect and other trades before first fix begins. Common conflicts: - Structural beams and joists that cannot be notched or drilled without engineer approval - Acoustic insulation in ceilings that must not be penetrated without acoustic detailing - Underfloor heating zones that define where floor penetrations are acceptable - MVHR ductwork that occupies ceiling void space needed for lighting circuits

Back box positions:

Every switch, socket, and data outlet position must be confirmed to the millimetre before installation — positions that look acceptable on a drawing may conflict with door swings, radiators, kitchen units, or fitted furniture. The electrical contractor should walk each room with the architect and interior designer to confirm all positions before fixing.

For lighting control systems (KNX, Lutron), the keypad positions are particularly sensitive — they are the visible face of the electrical installation and must be positioned with the same care as the ironmongery.

Conduit in plaster and concrete:

All wiring in plastered walls and concrete floors should run in conduit (oval PVC conduit for plaster runs, rigid conduit for slab), not direct-buried. Conduit allows individual circuits to be replaced without opening walls — relevant for a building expected to be occupied for decades.

Lighting Design

Lighting design is a separate discipline from electrical specification. The lighting designer — if one is appointed — produces a lighting design drawing that specifies the position, type, and control of every luminaire in the building. The electrical contractor then prices and installs to that design. On a prime London renovation without a dedicated lighting designer, the electrical contractor or interior designer typically performs this function.

Layered lighting:

The principle of layered lighting — combining ambient (general), task (functional), and accent (decorative) light sources in each space — is the foundation of good residential lighting design.

• —Ambient: General illumination of the room. Typically achieved with recessed downlights, surface-mounted ceiling fittings, or indirect cove/pelmet lighting. Not the sole light source in a well-designed room.
• —Task: Directed light for specific activities. Under-cabinet lighting in kitchens; reading lights beside beds and chairs; desk lighting in studies.
• —Accent: Light that draws attention to objects, art, or architectural features. Picture lights, shelf lighting, uplighting at the base of columns or planting.

A room with only downlights — the most common residential lighting failure — has flat, shadowless illumination that reads as commercial rather than domestic. The lighting plan must include a mixture of light sources at different heights.

Downlight specification:

Recessed downlights are the standard ambient light source in a prime renovation. Key specification decisions:

• —Aperture size: 70mm, 90mm, or 110mm aperture. Smaller apertures (70–75mm) are less visually obtrusive in the ceiling plane; larger apertures allow more powerful lamps and wider beam angles.
• —Trim finish: White, chrome, brushed nickel, or black to match the room's metalwork specification.
• —Fire rating: Fire-rated downlights (rated to maintain the fire resistance of the ceiling) are required where the ceiling separates floors or forms part of a fire-compartment. In a private dwelling, fire-rated fittings are required in ceilings below bedrooms and between floors.
• —Beam angle: Narrow spot (8–15°) for accent; medium flood (25–38°) for general illumination; wide flood (60°+) for very close-to-ceiling installation where a wider spread is needed.
• —CRI: Colour Rendering Index — minimum CRI 90 for all residential spaces; CRI 95+ for art, wardrobe, and any space where colour accuracy matters.
• —Colour temperature: 2700K (warm white) for living rooms, dining rooms, and bedrooms; 3000K for kitchens where a slightly crisper light aids food preparation; consistent within each zone.

Recommended suppliers for prime residential downlights: Astro Lighting, Davey Lighting, Nemo Lighting, Delta Light (Belgium), iGuzzini.

Feature lighting:

Pendant lights, chandeliers, and decorative wall lights are specified by the interior designer and sourced from specialist lighting suppliers. Electrical requirements must be confirmed in advance: the weight of a large chandelier may require a dedicated structural fixing; a large pendant requires a canopy-to-ceiling junction box that must be positioned precisely.

External lighting:

External lighting — entrance, garden, facade uplighting, step lighting — requires IP-rated (minimum IP44 for covered external areas; IP65 for direct rain exposure) fittings and, where buried in the ground, IP68 in-ground fittings. External lighting circuits should be on a separate zone and timer from internal circuits.

Specialist Electrical Systems

Data and AV cabling:

A structured cabling installation — Cat6a Ethernet and coaxial cables to every room, terminating in a central communications cabinet (patch panel, switches, routers) — is the backbone of the home network and AV distribution system. Wireless coverage is supplemented by PoE (Power over Ethernet) access points (Ubiquiti UniFi, Cisco Meraki) mounted flush in ceilings or walls.

USB and charging outlets:

USB-A and USB-C charging outlets integrated into socket faceplates (MK, Retrotouch, Hamilton) eliminate the cable adaptor clutter around desk and bedside areas. Specify USB-C PD (Power Delivery) outlets at desks and home office areas for laptop charging without bricks.

Garden power:

External sockets (IP66 rated, weatherproof covers), garden lighting circuits, and power for outbuildings should all be on RCD-protected circuits with circuits run in armoured cable (SWA) where buried in the ground.

Compliance and Certification

All electrical work in a domestic property must comply with BS 7671 (18th Edition Wiring Regulations). Notifiable work — new circuits, consumer unit replacement, work in kitchens and bathrooms — must be certified by a Part P competent person or inspected and certified by Building Control. The electrical contractor must provide an Electrical Installation Certificate (EIC) at completion, covering every circuit installed.

A full Electrical Installation Condition Report (EICR) on the existing installation before works begin establishes the baseline — relevant for insurance purposes and for identifying any pre-existing defects that must be remedied.

Cost Guidance

Electrical installation costs for prime London renovation:

• —Full rewire (large Victorian terraced house, 5 bedrooms): £25,000–£55,000
• —Consumer unit upgrade only: £2,000–£5,000
• —Lighting design (specialist consultant): £5,000–£20,000 depending on scope
• —Structured data cabling (Cat6a, patch panel, APs): £8,000–£20,000
• —EV charger installation (7kW, dedicated circuit): £1,200–£2,500

These are base electrical costs; lighting control systems (Lutron, KNX) are priced separately as they overlap with the building automation scope.